A retrospective study (2006-2020) of biopsy cases in pet guinea pigs (Cavia porcellus), degus (Octodon degus) and chinchillas (Chinchilla lanigera) at an exotic animal clinic in Tokyo, Japan.

Hystricomorphs, such as guinea pigs (Cavia porcellus), degus (Octodon degus) and chinchillas (Chinchilla lanigera), have become increasingly popular pet animals in Japan. However, comprehensive data on diseases in these animals remain limited, primarily restricted to single case reports, except for guinea pigs. The present study aimed to investigate the frequency of neoplastic and non-neoplastic diseases in pet guinea pigs, degus and chinchillas in Japan and to describe their epidemiological characteristics. We reviewed biopsy samples from guinea pigs (n = 134), degus (n = 57) and chinchillas (n = 16) collected at the Miwa Exotic Animal Hospital and the Laboratory of Veterinary Pathology, University of Tokyo, between 2006 and 2020. The most common condition in guinea pigs was integumentary disorders (n = 83; 61.9%), with mammary carcinoma (n = 41; 49.1%) being the most prevalent. The second most common condition was female reproductive disorders (n = 43; 32.1%), with ovarian cysts (n = 11; 25.6%) the most frequent. In degu samples integumentary disorders (n = 23; 40.3%) were the most common, followed by respiratory disorders (n = 22; 38.5%). Soft tissue sarcoma (n = 15; 65.2%) was the most frequently observed integumentary disorder, while fibroma with bone formation (n = 10; 45.4%) was the most prevalent respiratory disorder. In chinchilla samples female reproductive disorders (n = 13; 81.2%) were the most common, with endometritis being the most frequent (n = 5; 38.4%). The frequency of disorders peaked at 3-4 years old in guinea pigs and degus. No age-specific peaks were observed in chinchillas. This is the largest retrospective histopathological study on degus and chinchillas to date and the findings provide valuable insights for veterinarians treating hystricomorphs.